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Structure of the brain and ventricular system
The brain
Parts of the brain
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Composed of the cerebrum, cerebellum and brainstem
Cerebral cortex has gyri (folds), sulci (grooves) and fissures (clefts)
Overall size of brain is consistent between individuals, while sulci and gyri vary

Cerebrum
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Includes cerebral hemispheres and basal ganglia
Cerebral hemispheres are the two sides of the brain separated by the
longitudinal cerebral fissure
Each hemisphere divided into four lobes – frontal, parietal, occipital, temporal
o Lobes related to overlying bone; boundaries don’t exactly correspond
Sulci divide up the lobes
o Central sulcus separates the frontal from parietal lobes
o Lateral sulcus on either side delineates the temporal lobe
o Parieto-occipital sulcus separates parietal from occipital lobes
Most anterior parts of frontal and temporal lobes are the frontal and temporal
poles, and the most posterior part of the occipital lobe is the occipital pole
Frontal lobes occupy the anterior cranial fossae, the temporal lobes occupy
the lateral parts of the middle cranial fossae and the occipital lobes extend
posteriorly over the tentorium cerebelli

Diencephalon
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Forms central core of the brain
Comprises
o Epithalamus (contains pineal gland)
o Dorsal thalamus
o Hypothalamus

Brainstem
1
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Pons
 Located in-between midbrain and medulla, in anterior part of posterior
cranial fossa
 CN V associated
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midlandstech
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midlandstech
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htm

Taken from wisegeek
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wisegeek
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htm

Ventricular system of the brain
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Four ventricles in the brain, filled with CSF
CSF secreted by the choroid plexuses of the ventricles, and also fills the
subarachnoid space and the spinal cord

Ventricles
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Lateral (1st and 2nd) ventricles are the largest
o Anterior horn
o Posterior horn
o Inferior horn
o Body
Third ventricle is a slit-like cavity between the two halves of the dicephalon
o Singular, narrow space
o Located between the two thalami
Fourth ventricle is pyramid shaped, located in the posterior pons and medulla
o Tapers into narrow channel; connects to cervical region of spinal cord
Connections between ventricles
o Each lateral ventricle opens through an interventricular foramen into
the third ventricle
o Third and fourth ventricles are connected by the cerebral aqueduct
(narrow channel in the midbrain)
CSF drains from the fourth ventricle into a median aperture and paired lateral
apertures to the subarachnoid spaces

Subarachnoid cisterns
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At certain sections in the base of the brain, the arachnoid and pia are
separated by subarachnoid cisterns, containing CSF and soft tissue structures
(anchor brain; e
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arachnoid trebeculae, vasculature, cranial nerve roots)
Major cisterns
o Cerebromedullary cistern
 Located between cerebrum and medulla; largest cistern
 Receives CSF from fourth ventricle
 Posterior and lateral portions
o Pontocerebellar cistern
o Interpeduncular cistern
o Chiasmatic cistern
o Quadrigeminal cistern
o Cisterna ambiens

Taken from ABC Radiology Blog, Brain Ventricular System, available at
http://abcradiology
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co
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html

Secretion of CSF
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Similar to plasma, but less protein and no cells
Secreted by choroid epithelial cells (modified ependymal cells) in the
choroid plexuses of the lateral, third and fourth ventricles
Choroid plexuses comprise fringes of vascular pi mater (tela choroidea)
covered by cuboidal epithelial cells

Circulation of CSF
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Leaves lateral ventricles via interventricular foramina into third ventricle
Then passes via cerebral aqueduct to the fourth ventricle
From the fourth ventricle
o Some CSF leaves via the medial and lateral apertures into the
subarachnoid space (two lateral and one medial aperture)
o Most CSF flows to interpeduncular and quadrigeminal cisterns
CSF from subarachnoid cisterns flows through sulci and fissures on medial and
superolateral surfaces of the cerebral hemispheres
CSF also passes into extensions of subarachnoid space around cranial nerves

Absorption of CSF
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Main site of CSF absorption into venous system is the arachnoid granulations
Subarachnoid space containing CSF extends into core of arachnoid
granulations
CSF enters venous system via
o Transport through cells of the arachnoid granulations into the dural
venous sinuses
o Movement between cells making up the arachnoid granulations

Functions of CSF
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Protects brain from blows to the head (cushioning)
Nourishment of the brain
Buffering action – physical and chemical
Communication – hormones can travel in it
Buoyancy - CSF in subarachnoid space prevents weight of brain from
compressing the cranial nerves and blood vessels against the cranium
As the brain is heavier than the CSF, the gyri on the base of the brain contact
the floor of the cranial cavity when person is standing; superior part of brain
will have CSF in the subarachnoid space
Small rapidly recurring changes in intercranial pressure occurs from heartbeat
Slow recurring changes occur from unknown causes
Momentary large changes in pressure can occur from coughing and straining
when changing position
Changes in volume of intercranial contents e
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tumour, blockages can
change pressure - Monroe-Kellie doctrine

Lumbar spinal puncture
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Lumbar puncture/spinal tap is withdrawal of blood from the lumbar cistern
Important diagnostic tool for evaluating CNS disorders
o Infections e
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meningitis
o MS – pick up proteins and Ig in CSF
CNS disorders may change constitution of chemical constituents or introduce
cells into the CSF; can also determine if blood is present
Performed with the patient lying on the side with back and hip flexed (kneechest position)
Flexion of the vertebral column facilitates insertion of the needle by spreading
apart the vertebral lamina and spinous processes, stretching the ligament
flava
The skin covering the lower lumbar vertebra is anaesthetised and lumbar
puncture needle is inserted in the midline between the spinous processes of
L3 and L4 or L4 and L5 vertebrae
Note that a plane transecting the highest points of the iliac crests (supracristal
plane) passes through the L4 spinal process
No danger of damaging the spinal cord at this level; spinal cord tapers away
at L1/L2, so aim for L3/L4 level
o Lumbar nerves are just floating in CSF below this level, so will just float
out of the way (cauda equina)
Needle passes through the ligamentum flavum, dura and arachnoid to enter
lumbar cistern
Can get a low pressure headache after a lumbar puncture
Inspection of CSF macroscopically – should be clear, colourless; pathological
if cloudy, coloured, bloody; lab investigation to confirm composition
In foetus the spinal cord and column are matched in length; bony vertebral
column grows faster than the nervous tissue – known as foreshortening

Contraindication to lumbar puncture
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Increased intracranial pressure
o This is because as the CSF drops in the spinal column, the mass and CSF
will shift toward the low pressure outlet
o Brain would be sucked through the foramen
o This can cause trans-tentorial or uncal herniation
o Coning is a type of herniation where the brain stem is crushed through
the foramen magnum
o Symptoms of increased intracranial pressure are morning headache,
visual disturbances, papilledema (swelling of optic disc), nausea
o Increased intracranial pressure assessed by CT scanning or
examination of the fundus - see papilledema
Aggression/delirium
Skin infection
o Can spread to the CSF if infected skin is pierced

Taken from Kidshealth
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org/en/parents/lumbar-puncture
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5% of weight
Blood supply derived from internal carotid and vertebral arteries
Venous drainage is via cerebral and cerebellar veins that drain to the dural
venous sinuses

Internal carotid arteries
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Arise from the common carotids in the neck
Enters cranial cavity via carotid canal (petrous part of temporal bone)
o Carotid canal also contains venous plexuses and carotid plexuses of
sympathetic nerves
Internal carotids course anteriorly via cavernous sinuses with the abducent
nerves (CN VI), close to oculomotor (CN III) and trochlear (CN IV) nerves
Terminal branches are the anterior and middle cerebral arteries, which are
connected by the anterior communicating artery
Internal carotids joined to the posterior cerebral arteries via the posterior
communicating arteries - makes the cerebral arterial circle (of Willis) around
the interpeduncular fossa
Known as the anterior circulation of the brain

Vertebral arteries
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First branches of the subclavian arteries; left is usually larger than right
Cervical parts of the vertebral arteries ascend through the transverse
foramina of the first six cervical vertebrae
The atlantic parts of the vertebral arteries (sections assoc with C1, atlas) pass
through dura and arachnoid and through the foramen magnum
The two vertebral arteries unite at the intracranial part (caudal border of
pons) to form basilar artery
o Basilar artery ends by dividing into the two posterior cerebral arteries
Posterior circulation of the brain

Cerebral arteries
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Cortical branches supply deep parts of the brain and also surface and poles
of the cerebrum
o Anterior cerebral – most medial and superior surface, and frontal pole
o Middle cerebral – lateral surfaces and temporal pole
o Posterior cerebral – inferior surface and occipital pole

Cerebral arterial circle (of Willis)
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Pentagon shaped circle of vessels on ventral surface of brain
Formed by the following anastomosing arteries
o Anterior communicating
o Posterior communicating
o Anterior cerebral
o Posterior cerebral
o Internal carotid

Taken from blogs
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com, Happy Birthday, Circle of Willis, available at
http://blogs
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com/mind-guest-blog/happy-birthday-circle-of-willis/

Taken from Moore et al, Clinically Oriented Anatomy, Seventh Edition

Taken from studyblue
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studyblue
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wikia
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g
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g
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Moore et al
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Seventh Edition

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